Collision-induced dissociation studies of protonated alcohol and alcohol-water clusters by atmospheric pressure ionization tandem mass spectrometry. 1Methanol

Cluster size distribution and collision‐induced dissociation (CID) studies of protonated methanol and protonated methanol—water clusters yield information on the structure and energetics of such ions. Ions were formed at atmospheric pressure in a corona discharge source, and were subjected to CID in the center quadrupole of a triple quadrupole mass spectrometer. Cluster ions containing up to 13 molecules of methanol and/or water were observed and examined using CID experiments. The CID of all (CH3OH)n · H2O · H+ clusters, where n ⩽ 8, showed that water loss was statistically favored over methanol loss and that the preferred dissociation channel involved loss of water with methanol molecules. These results support a model employing a chain of hydrogen‐bonded solvent molecules rather than one in which fused rings of ligands surround a central hydronium ion. However, CID of larger clusters, where n ⩾ 9, showed that loss of one methanol was equal to or less than loss of water, reflecting a change in structure.